Isolation of dominant seizure foci by multiple subpial transections.

Dominant seizure foci (DSF) are seizure foci that do not respond to multiple subpial transections (MST). DSF were isolated in 15/31 patients who underwent MST in the past 6 years. These patients had MST over both hemispheres (6 patients) or over multiple lobes of one hemisphere (9 patients). DSF measured 0.5-1 cm in diameter and numbered 1-4 (in each patient). Their excision resulted in dramatic improvement in EEG over wide areas of the cortex. The longest postoperative follow-up is 67 months, with a median of 21 months. Nine of 15 patients are free of seizures, 3/15 have rare seizures, 2/15 have > 90% reduction in seizure frequency, and 1/15 has > 70% reduction in seizure frequency with improvement in motor and speech functions. In summary, DSF are resistant to MST and influence the electrical activity of the surrounding cortex. MST combined with excision of DSF resulted in good seizure control in this series, which included patients with multilobar and bihemispheric seizure foci.